The present invention relates to a method for the manufacture of a composite of an ion-exchange membrane and a catalytic metal having a strong adhesive property between the ion-exchange membrane and the catalytic metal (electrode) and a low contact resistance.
Composites comprising an ion-exchange membrane and a catalytic metal (hereinafter abridged simply as I-C composites) have been conventionally utilized in water electrolysis, brine electrolysis, hydrochloric acid electrolysis, fuel cells and so forth in which use is made of a solid polymer electrolyte (hereinafter referred to simply as SPE).
In the art of such electrolysis, it has been a matter of a particular importance to improve the adhesive property between the ion-exchange membrane and the catalytic metal in order to have the voltage required for electrolysis or decomposition reduced and the energy efficiency enhanced. That is to say, if insufficient is the adhesive strength between the ion-exchange membrane and the catalytic metal, this leads disadvantageous results such as a rise in the electrolysis voltage due to a high contact resistance present across the attached surfaces of the membrane and the metal, a peeling of the catalyst metal off the membrane, and so forth.
For the manufacture of I-C composites, methods are known, for example such a one as disclosed in Japanese Patent Laid-Open Publication No. 52-78788, in which catalytic powder is attached onto a membrane under a high pressure and at a high temperature with use of a binder such as Teflon for example, and a one as shown in Japanese Patent Publication No. 42-5014 and Japanese Patent Laid-Open Publication No. 55-38934, in which a catalytic metal is directly deposited on a membrane with use of a reducing agent and a metal salt solution.
With the composites manufactured according to those methods, however, the adhesion between the ion-exchange membrane and the catalytic metal does not comprise a chemical adhesion but comprises a physical one based on the van der Walls force for example, and generally the compsites have only a poor adhesive property and, as before mentioned, show a high contact resistance, making an accordingly high electrolysis voltage required.